The current invention relates to position tracking and machine control systems and, in particular, to a combination of a laser system and a global navigation satellite system to track the position of a machine and to provide accurate control of the machine based on the tracking information.
Global navigation satellite systems (hereinafter collectively referred to as GNSS), like GPS, and GLONASS, have been used extensively to determine position coordinates. Such position coordinates can be used in surveying operations, and for automated control of mobile units. In the future, the European GALILEO system will have similar capabilities. An autonomous navigational system that includes a satellite receiver and a navigational computer can achieve a 10-meter level of accuracy in determining the position of a mobile unit using solely the satellite signals. Differential navigational systems that utilize differential corrections in addition to the satellite signals can determine the positional information to within a meter range of accuracy. Real-time kinematic (RTK) navigational systems that are capable of utilizing both code and carrier information transmitted from such satellites can achieve centimeter level accuracy.
While such GNSS systems are capable of monitoring the movement of mobile equipment and operating as a part of a system that controls the operation of such equipment, such as for example graders and other types of earthmoving equipment, global navigation satellite systems cannot operate effectively when satellites are blocked or partially blocked from view. Optimally, such global navigation satellite systems receive data from all satellites in view and calculate the position of the receiver based all satellites. Such systems are capable of operating when receiving transmissions from only four satellites, or when satellite geometry is weak (the geometric dilution of precision is high), however system positioning accuracy and performance will degrade. It is clear that when fewer than four satellites are being received, or when more than four satellites are tracked but the satellite geometry is weak, the control of the system must be achieved in an alternative manner. Further, in some instances, even when transmissions from five satellites are received, the accuracy achievable is less than desired.